Chapter 5: Molecules & Compounds
molecular models
- 3D representations of molecules are used to represent compounds using the ball-and-stick & space-filing models
Joseph Proust's Statement of Law of Constant Composition
- A scientist named (blank) alive from (1754-1826) formally stated the idea that elements combine in fixed proportions to form compounds -A (blank) law states: all samples of a given compound have the same proportions of their constituent elements
space-filling model
-(blank) atoms fill the space between each other to more closely represent our best idea for how a molecule might appear if we could scale it to a visible size
Chemistry in the Environment:Acid Rain
-(blank) occurs when rainwater mixes with air pollutants- such as NO, NO2, & SO2- that form acids -NO & NO2 primary from vehicular emission, combine with water to form HNO3 (aq) -SO2, primary from coal-powered electricity generation, combines with H2O & oxygen in air to form H2SO (aq) -HNO3 (aq) both cause rainwater to become acidic - when (blank) flows into lakes & streams, some species of aquatic animals cannot tolerate the increased acidity & die a) (blank) weakens trees by dissolving nutrients in the soil & damaging their leaves b) (blank) also damages building materials
structural formula
-(blank) use lines to represent chemical bonds & shows how atoms in a molecule are connected to each other
Binary Ionic Compounds with metal of invariant charge
-Binary compounds: contain only 2 different elements. The names for binary ionic compounds containing a metal that forms only one type of ion have this form: Name of cation (metal)---> base name of anion (nonmetal) + -ide *since the charge of the metal is always the same for these types of compounds, it need not be specified in the compound's name EX: name NaCl, consists of the name of the cation, sodium followed by the base name of the anion, chlot, with the ending -ide. NAME: Sodium Chloride
Salt's properties differ from those of the Elements Na & Cl that make up salt
-Elemental Na: is extremely reactive metal that dulls almost instantly upon exposure to air -Elemental Cl: is a yellow gas with a pungent odor. It is highly reactive & posionous -NaCl is the compound formed by Na & Cl-- Table salt
Common Chemical Formulas
-NaCl for table salt, indicating Sodium & Calcium atoms in a 1:1 ratio -CO2 for carbon dioxide, indicating Carbon & Oxygen atoms in a 1:2 ratio -C12H22O11 for table sugar (sucrose), indicating Carbon, Hydrogen, & Oxygen atoms in a 12:22:11 ratio - the subscripts in a chemical formula represent the relative number of each type of atom in a chemical compound; they never change for a given compound
Sugar's properties differ from those of the elements C,H, & O that make up sugar
-Ordinary table sugar is a compound called sucrose. a) a sucrose molecule contains C,H, & O atoms b) the properties of C, such as graphite, H & O.
Molecular formula (types of chemical formula)
-a (blank) gives the actual number of atoms of each element in a molecule of the compound EX: for hydrogen perioxide is H2O2, & it empirical formula is HO a) the (blank) is always a whole-number multiple of the empirical formula
Rules to make a chemical formula (continued)
-among non-metals, those to the left in the periodic table are more metal-like than those to the right & are normally listed first a) we write NO2 & NO, not O2N & ON -within a single column in the periodic table elements toward the bottom are more metal-like than elements towards the top a)we write SO2, not O2S
Empirical formula (types of chemical formula)
-an (blank) gives the relative number of atoms of each element in a compound
Elements may be atomic or molecular
-atomic elements are those that exist in nature with single atoms as their basic units. Most elements fall into this category. -molecular elements do not normally exist in nature with single atoms as their basic units. Instead, these elements exists as diatomic molecules-- 2 atoms of the element bonded together-- as their basic units
Naming binary acids
-binary acids are composed of hydrogen & a nonmetal FORM: Hydro--->base name of nonmetal+ -ic---> acid EX: HCl (aq) is hydrochloric acid HBr (aq) is hydrobromic acid HCl (g) to hydrogen chloride molecules in a gas phase, & not the acid H2S (aq) is hydrosulfuric acid
Rules to make a chemical formula
-chemical formulas list the most metallic elements first a) the formula for table salt is NaCl not ClNa -in compounds that do not include metal, the more metal-like elements are listed first a) metals are found on the left side of the periodic table & nonmetals on the upper right side
Nomenclature (naming compounds)
-chemists have developed systematic ways to name compounds -if you learn the naming rules, you can examine the formula of a compound & determine its name & vise versa a) many compounds also have a common name -H2O has the common name water & the systematic name, dihydrogen monoxide a) since water is such a familiar compound, everyone uses its common name, water, & not is the systematic name -common names can be learned only through familiarity; there is no system
Chemical Formulas: How to Represent Compounds
-compounds have constant composition with respect to mass because they are composed of atoms in fixed ratios -a chemical formula indicates the elements present in a compound & the relative number of atoms of each a) EX: H2O is the chemical formula of water; it indicates that water consists of hydrogen & oxygen atoms in a 2:1 ratio
Formula Mass: The Mass of a Molecule or Formula Unit
-for any compound the formula mass is the sum of the atomic masses of all atoms in its chemical formula formula mass= (# of atoms of 1st element in chemical formula X atomic mass of 1st element) + (# of atoms of 2nd element in chemical formula X atomic mass of 2nd element)
More info on chemical formulas
-for many compounds, such as H2O, the molecular formula is the same as the empirical formula
Naming Ionic compounds containing halo-oxyanions
-if there are more than 2 ions in this series, then the prefixes hypo-, meaning "less than" & per-,meaning "more than," are used ClO- hypochlorite BrO- hypobromite ClO2- chlorite BrO2- bromite ClO3- chlorate BrO3- bromate ClO4- perchlorate BrO4- perbromate IO- hypoiodite IO2- iodite IO3- iodate IO4- periodate -make sure to include ION in answers
Expections to note when naming molecular compounds
-if there is only 1 atom of the 1st element, the prefix mono- is normally omitted. CO2 no mono it is carbon dioxide -the compound N2O (AKA laughing gas) is named according to the 1st element, N, with the prefix di-, followed by the base name of the 2nd element, ox, prefixed by mono-, & the suffix, ide a) since mono- ends with a vowel & oxide begins with a vowel, an O is dropped & the two are combined as monoxide b) the entire name dinitrogen monoxide -when the prefix ends with a vowel & then the base name starts with a vowel, the 1st vowel is sometimes dropped a) vowel is dropped in monoxide but not in dioxide or triodide
Compounds may be molecular or ionic
-molecular compounds: formed from 2 or more nonmetals, the basic units of molecular compounds are the molecules composed of constituent atoms -ionic compounds contain 1 or more cations paired with one or more anions a) in most cases, the cations are metals & the anions are nonmetals
Naming Oxyacids
-oxyacids are acids that contain oxyanions- found in the table of polyatomic ions EX: HNO3 (aq) contains the nitrate (NO3-) ion H2SO3 (aq) contains the sulfite (SO32-) ion H2SO4 (aq) contains the sulfate (SO42-) ion -these acids are a combinatoin of one or more hydrogen ions with an oxyanion -the number of hydrogen ions depends on the charge of the oxyanion, so that the formula is always charge neutral
Molecular View of Elements and Compounds
-pure substances may be either elements or compounds -elements may be either atomic or molecular -compounds may be either molecular or ionic
Writing formulas
-review the elements that form ions with a predictable charge -ionic compounds always contain + & - ions -in a chemical formula, the sum of the charges of the + ions (cations) must ALWAYS equal the sum of the charges of - ions (anions) -write the symbol for the metal & its charge followed by the symbol of the nonmetal & its charge -make the magnitude of the charge on each ion (without the sign) become the subscript for the other ion -if possible, reduce the subscripts to give a ratio with the smallest whole numbers -check to make sure the sum of the charges of the cations cancels the sum of the charges of the anions exactly.
Binary Ionic Compounds with metal whose charge may vary
-since the charge of the metal cation in these types of compounds is not always the same, the charge must be specified in the metal's name a) we specify the charge with a Roman numeral (in parentheses) following the name of the metal. EX: We distinguish between Cu+ & Cu2+ by writing a (I) to indicate the 1+ ion or a (II) to indicate the 2+ ion Cu+ Copper (I) Cu2+ Copper (II) -the full names for these types of compounds have the following form: name of cation--->charge of cation (metal) in roman numerals---> base name of anion (nonmetal) + -ide
How to represent compounds with polyatomic ions
-some chemical formulas contain groups of atoms that act as a unit -when several groups of the same kind are present, their formula is set off in parentheses with a subscript to indicate the number of that group a) many of these groups of atoms have a charge associated with them & are called (blank) -to determine the total number of each type of atom in a compound containing a group within parentheses, multiply the subscript outside the parentheses by the subscript for each atom inside the parenthese
Naming ionic compounds containing polyatomic ions
-some ionic compounds contain polyatomic ions (ions that are themselves composed of a group of atoms with an overall charge) - EX: NO3:nitrate SO42-:sulfate NO2: nitrite SO32-:sulfite
Many natural substances are compounds
-some of the substances we encounter in everyday life are elements a) most are not elements-- they are compounds b) Free atoms are rare in nature -A compound is different from a mixture of elements a) in a compound, the elements combine in fixed definite proportions b) In a mixture, they can have any proportions whatsoever
Naming Molecular Compounds
-the 1st step in naming a molecular compound is identifying it as one a) remember nearly all molecular compounds form from two or more nonmetals -we learn how to name binary (two-element) molecular compounds. their names have the following form: Prefix--->name of 1st element--->Prefix--->base name of 2nd element + -ide -when writing the name of a molecular compound, as when writing the formula, the 1st element is a more metal-like one. The prefixes given to each element indicate the number of atoms present
Naming acids
-the 1st step in naming an acid compound is identifying it as one a) acids are molecular compounds that form ions when dissolved in water - they are composed of hydrogen, usually written 1st in their formula, & 1 or more nonmetals written 2nd - we can categorize acids into 2 groups: binary acids, those containing only hydrogen & a nonmetal, & oxyacids, those containing hydrogen, a nonmetal & O
Naming Ionic Compounds
-the 1st step in naming an ionic compound is identifying it as one a)Remember, any time you have a metal & one or more nonmetals together in a chemical formula, you can assume the compound is ionic.
Categorize Ionic compounds depending on the metal
-the 1st type (called Type I) contains a metal with an invariant charge-- one that does not vary from 1 compound to another -the 2nd type of ionic compounds (called Type II) contains a metal with a charge that can differ in different compounds a) such metals are usually (but not always) found in transition metals section of the periodic table -Some transition metals, such as Zn & Ag, form cations with the same charge in all of their compounds: Zn+2,Ag+ -some main group metals, such as Pb & Sn form more than one type of cation
Polyatomic ions in everday chemistry
-the active ingredient in household bleach is sodium hypochlorite, which acts to destroy color-causing molecules & kills bacteria -baking soda contains sodium bicarbonate (sodium hydrogen carbonate), which act as a source of CO2 gas in baking -Calcium carbonate is the active ingredient in antacids such as Tums & Alkamints. It neutralizes stomach acids -Sodium nitrite is a food additive used to preserve packaged meats such as ham, hot dogs, & bologna. sodium nitrite inhibits the growth of bacteria, especially those that cause botulism
Compounds may be molecular or ionic (continued)
-the basic units that compose dry ice, a molecular compound, are CO2 molecules -the basic units that compose table salt an ionic compound are NaCl formula units
Chemical Formulas: How to Represent Compounds (continued)
-the formula contains the symbol of each element, accompanied by a subscript indicating the number of atoms of that element. By convention, a subscript of 1 is omitted
Images make the connection between the world around us & the world of atoms & molecules
-the macroscopic world (what we see) -the atomic & molecular world (the particles that compose matter) -the atomic & molecular world (the particles that compose matter) -the symbolic way that chemists represent the atomic/molecular world
Comparison of Formulas
-the molecular formula of CH4 indicates that methane has 1 carbon atom & 4 hydrogen atoms -the structural formula shows how the atoms are connected: each hydrogen is bonded to the central Carbon atom -the ball-and-stick model & the space-filling model illustrate the geometry of the molecule: how the atoms are arranged in 3d
Important info about compounds
-the properties of a compound are, in general, different from the properties of the elements that compose it.
Changing a subscript makes a totally different compound
-the subscripts in a chemical formula are part of the compound's definition- if they change, the formula no longer specifies the same compound - CO is the chemical formula for carbon monoxide, an air pollutant with adverse health effects on humans. a) if you change the subscript of oxygen in the CO from 1 to 2, you get a totally different compound -CO2 is the chemical formula for carbon dioxide, the relatively harmless product of combustion & human respiration. We breathe small amounts of it all the time with no harmful effects
Exceptions to the list of nonmetal elements
-there are a few historical exceptions in which the most metallic element is named first, such as hydroxide ion, which is written as OH-
Mixtures
-this balloon is filled with a mixture of hydrogen & oxygen gas. the relative amounts of hydrogen & oxygen are variable.
Chemical compound
-this balloon is filled with water, composed of molecules that have a fixed ratio of hydrogen to oxygen
Binary Ionic Compounds with metal whose charge may vary (continued)
-we can determine the charge of the metal from the chemical formula of the compound a) the sum of all charges must be zero -the charge of iron in FeCl3 must be 3+ for the compound to be charge neutral with the 3 Cl- anions EX: the name for the compound FeCl3 is the name of the cation, iron, followed by the specific charge of the cation in parentheses (III), followed by the base name of the anion, chlor, with the ending -ide NAME of FeCl3: iron (III) chloride
Ball-and-stick
-we represent atoms as balls & chemical bonds as sticks a) the balls and sticks are connected to represent the molecule's shape. The balls are color coded, and each element is assigned a color
Prefixes for molecular compounds
1-mono 2-di 3-tri 4-tetra 5-penta 6-hexa 7-hepta 8-octa 9-nona 10-deca
Mass ratio of elements in ammonia is constant (example)
EX: if we decompose a 17.0 g sample of ammonia, a compound composed of nitrogen & hydrogen, we would get 14.0 g of nitrogen & 3.0g of hydrogen, of a nitrogen-to-hydrogen mass ratio of mass ratio= 14.0g N/3.0g H= 4.7 or 4.7:1 -even though atoms combine in whole-number ratios, their mass ratios are not necessarily whole numbers
Mass ratio of elements in water is constant (example)
EX: if we decompose an 18.0g sample of water, we would get 16.0g of oxygen & 2.0 g of hydrogen, or an oxygen-to-hydrogen mass ratio mass ratio= 16.0g O/2.0g H= 8.0 or 8.0:1 -this is true of any sample of pure water, no matter what it origin
Compound
a substance formed when the atoms of two or more elements are linked by chemical bonds in fixed, definite proportions EX: NaCl, CO2
Molecule
a substance formed when two or more atoms are joined in a specific arrangement by chemical bonds EX: 02, Br2, NaCl, CO2
Naming Oxyacids (outline)
Oxyacids: contains oxygen Either -ite name of oxyanion end in -ite: change to base name of oxyanion + -ous acid OR -ate name of oxyanion ends in -ate: change to base name of oxyanion + -ic acid
Name of some common oxyacids & their oxyanions
http://drcalef.com/Chem10/Chapter5/img61.html
Common Anions
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Common Polyatomic Ions
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some metals that form cations with different charges
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Ionic compounds
when a metal, which has a tendency to lose e, combines with a nonmetal, which has a tendency to gain e, 1 or more e transfer from the metal to the nonmetal, creating + & - ions that are attracted to each other a) a compound composed of a metal & a nonmetals considered ionic -the basic unit of ionic compounds is the formula unit -unlike molecular compounds, (blank) do not contain individual molecules but rather cations & anions in an alternating 3d array
Classification of Acids
Acids: Formula has hydrogen as 1st element Either Binary: contains only 2 elements or Oxyacids: contains oxygen
Order to List the Nonmetal Elements in Compounds
C-Crazy P-Patrick N-Needs H-Helpful S-Snow I- In Br- Bright Cl- Clear O- Open F-Fields
How to represent compounds with polyatomic ions (example)
Ex: Mg(NO3)2 indicates a compound containing one magnesium atom (present as the Mg2+ ion) & two NO3- groups Mg: 1= 1 Mg N= 1X2= 2 N O= 3X2= 6 0
Elements may be atomic or molecular (continued)
Ex: an atomic element: the basic units that compose mercury, an atomic element & a metal, are single mercury atoms a molecular element: the basic units that compose Cl, a molecular element, are diatomic Cl molecules, each composed of two Cl atoms
Diatomic Molecules
H2-hydrogen, N2-nitrogen, O2-oxygen, F2-fluorine, Cl2-chlorine, Br2-bromine, I2-iodine
